1. Field of the Invention
The present invention relates to improvements in the art of making bituminous substrates, such as road surfaces, employing hot mix asphalt.
2. Description of the Prior Art
Asphalt surface course has been used for many years for roadways. The hot mix asphalt (HMA) is comprised of sand as one component, an aggregate or mineral component, and asphalt. The type of aggregate may vary widely, but may include such materials as granite, quartz and limestone materials. Asphalt forms a continuous phase and acts as a binding agent for the mineral aggregate. The continued preservation of bond between the asphalt and rock or mineral content of the composition is necessary to insure a lasting pavement.
The use of hydrated lime, Ca(OH).sub.2, to treat the aggregate in HMA is well accepted technology to improve the performance of the asphalt/aggregate blend. The effects of lime as an anti-strip additive when lime is added directly to the aggregate are well established. Typically, dry hydrated lime is mixed with the aggregate. The lime promotes extended mixture life by improving the asphalt-aggregate bond and by reducing the susceptibility of the mixture to soften when water is absorbed within the mixture. Amounts used are 1-3% lime based on the total weight of HMA. The benefits of lime are believed to be the result of interaction between the inorganic aggregate and the organic bituminous asphalt binder.
While lime has been used by adding it directly to the aggregate prior to the addition of the asphalt binder, Applicants' are unaware of any work in which lime is added directly to the asphalt binder in quantities sufficient to act as a multi-function modifier with the binder then being added to treated or untreated aggregate.